Effect of fire regimes on the demographic parameters of the perennial tussock grasses of a humid savanna

Questions Perennial tussock grasses represent the principal fuel source for savanna fires; however, basic information about the impact of fire on their demography remains scarce. Do dominant perennial grass species differ in their demographic parameters? What is the overall impact of tussock circumference and fire regimes on grass demographic parameters? Do grass species differ in the sensitivity of their demographic parameters to fire regimes and tussock circumference? Location The study site is located in the savanna of the Lamto reserve, in the center of Ivory Coast (6 degrees 9 ' to 6 degrees 18 ' N, 5 degrees 15 ' to 4 degrees 57 ' E). Methods Data on the nine dominant species of tussock grasses were sampled over one year under four fire treatments (early fire, mid-season fire, late fire and no fire). We studied the impact of these fire treatments and tussock circumference on five demographic parameters: mortality, fragmentation (the division of a tussock into several smaller ones), growth, retrogression (the decrease in tussock size) and fecundity. Results All demographic parameters varied among species and across the fire regimes. Late fire had the largest negative effect on all parameters except fecundity. Schizachyrium platyphyllum was the most disadvantaged species by fire in terms of mortality, retrogression and growth, whilst Andropogon ascinodis was the most prone to fragmentation. Hyparrhenia smithiana and Sorghastrum bipennatum produced the most seeds and Brachiaria brachylopha produced the most new tussocks. The circumference of perennial grasses impacted all demographic parameters. Small individuals had the highest mortality and growth rates, while large individuals showed the highest fragmentation and retrogression rates, and produced the most seeds. Conclusions This study showed that perennial grass species differed in their sensitivity to fire treatments. Nevertheless, the mid-season fire could be advised to managers for the sustainable management of the Lamto savanna